According to Bill's book: Stu and Nicky - piano on Silver Train and Star Star, and Nicky with a questionmark on Angie (though I bet it's him, it's the same kind of romantic style he played on Lennon's Jealous Guy)
Billy is listed playin clavinet (100 years and Heartbreaker both start with clavinet). So it might well be Mick playin piano on this one.